Electrical control device



Nov. 18, 1941. N. c. scHELLENGl-:R 2,252,821

ELECTRICAL CONTROL DEVICE Filed July 17, 1939 2 Sheets-Sheet 1 55 /D//ES/VE 4 OBR/CHN 7' f2 F 'y 3 56' HOHES/VE OBR/CH/VT Lm" H-l N0 18, 194l- N. c. scHELLENGER ELECTRICAL CONTROL' DEVICE Filed July 17, 1939 2 Sheets-Sheet 2 llllllllllll m J@ C l N www Patented Nov. 18, 1941 ELECTRICAL CONTROL DEVICE Newton C. Schellenger, El Paso, Tex., assignor to Chicago Telephone Supply Company, Elkhart, Ind., a corporation of Indiana Application July 17, 1939, Serial No. 284,840

(Cl. 20L-48) 9 Claims.

This invention relates to a new and improved combination electrical control device of the type illustrated in the copending application of Newton C. Schellenger, Serial No. 602,006, filed March 30, 1932 now Patent No. 2,198,277, of which this application is a continuation in part. More particularly the present invention refers to a control device comprising a variable resistance unit combined with an electric switch unit, both of which are arranged to-be operated by a single rotatable shaft, the two units being electrically shielded from each other by a fixed metallic Wall. y

Such combination devices are widely used in radio apparatus, public address systems, electrical test apparatus and the like. The variable resistance is employed in radio circuits to control the volume of sound emitted by the loud speaker, and the switch unit, in the form of a snap switch, is normally employed to open or close the electric power circuit which supplies power, usually in the form of alternating current, to the radio circuit. Where the word switch is used herein, it is to be understood that reference is made to what'is commonly known as a snap switch suitable for controlling such circuits.

Combination controls of this general type have been commonly employed in radio receiving sets for some time. However, as such sets have, from year to year, been made progressively of higher sensitivity and also more compact with parts smaller and closer together, continued improvement in the effectiveness of the electrical shielding between the variable resistance and the switch has been necessary. Therefore, my present invention, which is another step forward in this fast developing art, is primarily concerned with achieving complete'electrical shielding between the switch and the variable resistance by providing a structure for accomplishing this end which will enable the variable resistanceswitch manufacturer to produce such a unit commercially at a cost that will enable him to supply the trade with a. better product at no increase over prevailing prices.

In this new structure as shown and described herein, I have been able to overcome inherent weaknesses which are present in the now generally used types of variable resistance switch combinations substantially all of which employ a metallic switch operating member or cam extending from within the switch housing through a relatively large, eccentrically located hole in the electrostatic shield, into the variable resistance chamber where the switch operating member is brought into Yoperative relationship with the switch actuator. The principal diillculty experienced with this type of variable resistance switch combination is due to the necessarily imperfect shielding between the highly sensitive variable resistance circuit and the interference producing, switch power circuit. With such a structure, interference radiation passes from the switch chamber, through the above mentioned hole in the electrostatic shield to the variable resistance circuit, causing power circuit noise or ripple to be annoyingly reproduced by the loud speaker of the radio set. Further. the switch operating member, even when well insulated from the switch circuit, will pick up charges radiated within the switch housing by the switch circuit and then reradiate such electrical disturbances in the variable resistance chamber, causing power circuit interference to again reach the variable resistance circuit and be reproduced by the loud speaker.

By locating all switch parts Wholly within a grounded metallic switch housing and eliminating all holes in the electrostatic shield between the switch and the variable resistance, through which interfering radiation could pass from the switch to the variable resistance, I have achieved a variable resistance-switch combination in which the sensitive variable resistance 4circuit is perfectly shielded from the interfering influences of the closely associated switch circuit.

In control devices of the character herein described considerable difiiculty has been encountered in arranging the shaft and associated elements to insure proper alignment and free, smooth unhampered rotation of the operating shaft without its having any tendency toward binding when the device has been finally fastened to the radio chassis by the usual threaded thimble and mounting nut.

In my improved construction the end wall of the metallic variable resistance housing is provided with a centrally located circular opening having a rim extruded downward inside the variable resistance housing in order to provide a close fitting sleeve bearing for the cylindrical bearing portion of the shaft adjacent its upper end. A second bearing is provided at the extreme lower end of the thimble and being spaced as far as possible from the bearing in the housing end wall in order to provide the greatest amount of support for the shaft. With two lrelatively short bearings spacedat opposite ends of the control it is possible to successfully employ lshowing the means for shorter mounting bushings without the shaft having objectionable side play. In the present .construction I have reduced the diameter of the yshaft will turn freely in these two bearings and stillhave no objectionable side play or looseness.

It is the principal object of the present invention to provide a combination variable resistance and switch device in which the switch and variable resistance units are combined for joint operation with complete electrical shielding therebetween.

It is also an object to provide such a device which is small in size and in which a fixed metallic wall is interposed between the units,separat ing them by a complete shield.

It is an additional object to provide a combination device in which the switch constr'uction is located wholly within a switch housing with no parts extending within the associated variable resistance chamber or housing.

It is another object to provide a construction in which a switch actuator is carried within the switch housing upon the outer face of the end wall of the housing of the variable resistance unit and associated with the shaft of said unit for operation therewith.

It is also an object to provide in such a combination, a switch housing having means formed therein for maintaining both the switch and switch actuating means in desired relation to the switch housing and to each other.

It is another objectof the present invention to provide a combination device comprising a switch and a variable resistance in which the switch and variable resistance units are not only shielded from each other but in which both units are individually shielded in grounded metallic housings constituting electrostatic shields which are substantially continuous with the exception of the necessary openings for terminals.

It is an additional object to provide a compact device of 4this character which is composed of but few parts and adapted for commercial assembly and use.

Other and further objects will'appear as the description proceeds.

I have shown a preferred embodiment of my y invention in the accompanying drawings, in

whichy Figure 1 is an elevation of a switch and variable resistance combination device embodying the present invention withy the housings shown in section and portions of the units broken away;

Figure 2 is a transverse section taken on a line 2-2 of Figure 1 and partly broken away to better show the relationship of the parts;

Figure 3 is a perspective view of the form of actuator shown in Figures 1 and 2;

Figure 4 is a face view from below of the switch and switch housing assembly, the actuator being removed for clarity;

Figure 5 is a plan view of the outer face of the switch and switch housing assembly;

Figure 6 is a perspective view of the inner or switch operating end of the variable resistance shaft;

Figure 7 is a fragmentary vertical section connecting the switch housing to'the outer face of the end wall O1 the variable resistance housing; and

Figure 8 is a fragmentary transverse section taken on line 8-8 of Figure 7.

While the present invention relates particularly to the shielding construction between a variable resistance or other control unit and an associated switch and the driving connection between the units, it is necessary to briey describe the switch and variable resistance or rheostat construction shown, in order that the operation of the combination may be understood. The present invention does not relate, however, to details of construction of either the switch or the variable resistance per se, but to the provision of a fixed metallic shield between the two with the openings therein completely closed, `and to the driving connection for joint operation of the units. The general switch construction shown and described herein is covered in my copending application Serial No. 83,963, led June 6, 1936, while the variable resistance construction is generally the same as that shown and covered in my copending application Serial No. 218,062, led July 8, 1938.

'I'he rheostat or variable resistance comprises a base II formed of insulating material, the main body of the'base being substantially circular in form with a terminal portion IIa extending therefrom. The arcuate resistance element i2 is supported upon the base II. The end terminals I3 and Il are secured to the respective ends of the resistance element by the rivets I5 and I6 which extend through the terminal portion IIa of the base and secure the resistance element I2 and terminals to the base. The base II is provided with a central opening through which the threaded metallic thimble or bushing l1 extends, with its cylindrical portion I'Ia tted in the opening. The innerend of the thimble has the enlarged head I8 which bears against the inner face of the base ii within the arcuate resistance strip I2. The metallic ground plate I9 lies against the outer face of the base II and is held in position by the spacing washer 20. The thimble portion IIa has a shoulder ZI swedged into the spacing washer 20- to firmly secure the base Il, ground plate i9 and spacing washer 20 together. This connection further serves to electrically connect the grounding plate to the thimble or bushing I1. The thimble Il serves as a mounting means for the entire unit as its threaded extension may be passed through an opening in a chassis wall or other support and secured in place by a nut screwed thereon.

The variable resistance shaft 22 is rotatably fitted into the thimble Il, the shaft having a short bearing portion 23 engaging the wall of the bore in the thimble adjacent the outer end o1' the thimble, as shown in Figure l. This bearing is of limited extent in a direction parallel to the axis of the shaft, the greater portion 22a of the shaft within the thimble being of lesser diameter than this bearing portion 23 to provide a clearance as shown at 24. Movement of the shaft 22 inwardly of the unit, or upwardly as seen in Figure l, is prevented by a C-washer 25 tted in a circumferential groove 26 in the shaft, the washer engaging the outer end of the thimble I1.

As shown in Figure 6, the shaft 22 has a shoulder 21 adjacent its upper end below the reduced i tion 28 is iiattened on opposite sides as shown at 28a so that it positively drives the stop plate 30. fitted upon this portion 23. The shoulder 3| between this portion 23 and the reduced bearing portionl 33 of the shaft is swedged over onto the stop plate to secure the stop plate positively to the shaft 22. The stop plate 30 has a downturned driving ear 32 which fits in a notch in the drive arm 23 to cause that arm also to rotate with shaft 22. The shaft 22 has the upper cylindrical bearing portion 33 which is smaller than the main portion of the shaft.

The contact arm 34, formed of resilient metal is caused to rotate with the driving arm 29 by means of the ears 35 fitting into notches in the arm. The contact arm is provided with the spaced spring contact fingers 36 and 31 which resistance housing 42 by means of ears 52 extendengage the upper face of the resistance element g i2, and is further provided with the brushportion 33 making contact with the metal collector ring 33. The collector ring is formed with an integral extension 39a which connects it to the center terminal 4|. This collector ring 39 is insulated from the headof the metallic thmble or bushing i1 by a washer 40 formed of insulating material. f

The variable resistance or rheostat is enclosed in a cup-shaped metallic housing 42 with a` cylindrical side wall and yhaving a fiat end wall- 43. The housing is provid'ed with an inwardly. embossed portion 44 serving to coact with the stop ear-30a on the stop arm 30 to limit rotation of the variable resistance contact structure. This housing is secured to the rheostat assembly by means of ears 45 which fit in notches 46 in the edge of the base and which are bent against the under face of the base. Other similar ears pass through slots 41 in the ground plate i3 to positively and firmly locate the housing and to pre'- vent its circumferential displacement relative to the ground plate and to the base. rI'his connection serves also to electrically ground the housing to the grounding plate and through the cular opening having the downwardly or inwardly extruded rim 43. 'I'he inner face 43a of the rim 43 serves as a bearing for the inner end of the shaft 22 and is of a .diameterv to properly fit and support the bearing portion 33 of the shaft. 'I'he shaft 22 has the flattened inner end portion 49, all of the edges of which are chamfered as shown at and 53a.

This flattened end portion 49 of the shaft drives the switch actuating plate 5| by projecting into an oblong or substantially rectangular central opening 52 therein, the plate structure being best shown in perspective in Figure 3. The plate 5| is provided with the upwardly extending lug 53 adapted to coact with the switch cam to operate the switch. The actuating plate 5I has a plurality of cut-out portions 54 which may dif'fer in size. These cut-out portions serve to carry and distribute an adhesive lubricant 55 which reduces the frictional wear between the parts and has the important function of holding the plate 5| against the outer face of the end wall 43 of the housing 42, preventing rattling of the actuator plate against the adjacent parts should the unit be subjected to vibration. v

The switch construction shown in Figures 1 and 4 comprises the insulating base 50 secured in the cup-shaped metallic housing 6 l. As best shown in Figures 2, 7 and 8, this housing 6| is secured to the outer face of the end wall 43 of the variable ing through rectangular slots 63 in the housingv wall 43 and bent up against the under face of this wall. The housing 6| is provided upon its side wall with inwardly extending ribs 54, the upper ends of which serve to retain the insulating base against the end wall 55 of the housing. The lower ends 63 of the ribs 54 are located closely adjacent the upper face of the switch actuatin plate 5|.

As shown in Figures land 5, the switch pivot 5l passes through end wall 65 of the housing 6| and also through the base 33 to assist in holding the parts together as well as to positively ground the pivot member to the switch housing. As best shown in Figure 5, the end wall 65 of the switch housing 5| is continuous with the exception of the necessary openings 55a and 65h for the terminals 12 and 13. These openings are kept as small as possible and allow only suiiicient clearance be'- tween the terminals 12 and 13 and the grounded switch housing end wall 65 to prevent the terminais shorting to the housing.

rI'he switch arm 31 is mounted on the pivot 53 and moves a U-shaped contactor 09 into and out of bridging engagement with the fixed contacts which comprise two studs 13 and 1| fixedly 5E- cured on the base by shanks extending through the base and riveted onto terminal members 12 and 13. A limited pivotal driving connection between the arm 51 and the contactor 63 is provided by the lug 69o fitting into opening 61h in the arm 61. The lugs 59a and 69h on the contacter fitting into opening 61a in the arm 61 serve to guide the contacter and limit its pivotal movement with respect to the arm around the driving connection. A metallic switch operating cam 14 is mounted on the pivot 65 above the switch arm 51. As shown in Figure 4, this cam 14 is limited in its rotational movement by the stop extension 15 on the lower leg 14a of the cam and by the connecting portion 11 of the cam, which alternately engage the inwardly formed emboss 13 in the side wall of the switch housing 5| adjacent the cam when the cam is at its opposite limits of movement. The switch cam 14 is connected with the switch arm 51 by a torsion spring 13 which serves to provide a spring toggle link for moving the switch arm and driving the movable contact 39 into and out of engagement with the fixed contacts 10 and 1| upon movement of the switch cam 14 in opposite directions.

As clearly shown in Figure 1, the lower ends 55 of the longitudinal ribs 64 in the side wall of the switch housing 5| are sheared from the body of the wall and extend over and closely Y above the outer portion of the switch actuating member 5I. 'I'hese lower ends 65 of the ribs. therefore, have the important function of limiting any movement of the disc 5| away from the outer face of the end wall 43 of the variable resistance housing. They prevent any movement of the member 5|k which would cause this member to bind in its movement or to get out of operative relationship with the flattened end 49 of the shaft 22, It will be understood that the lubricant placed between the member 5| and the outer face of the variable resistance housing wall 43 normally maintains the member 5| against that outer face by adhesion. Consequently the lower ends 35 of these ribs 54 are normally out of contact with the member 5|. They serve merely as limiting stops to prevent disengagement of the parts under jar or violent vibration and to facilitate the assembly of the parts.

The bearing 48a serves to centrally locate the portion 33 and consequently the fiattened end 49 of the shaft 22 in respect to the flat end wall V43 of the rheostat housing 42. The rectangular slots 63 in the end wall 43 of the'rheostat housing are so arranged as to centrally locate the cylindrical side Wall of the switch housing relative to the end wall ofthe rheostat housing thereby uniformly spacing the inner face of the cylindrical sidewall of the switch housing from the centrally located bearing 48 in the end wall 43 of the rheostat housing. This' is accomplished by locating the edges of the slots 63 toward the center of the end wall of the rheostat housing upon a diameter corresponding to the diameter of the inner face of the cylindrical side wall of the switch housing. Consequently the inner faces ofthe ears B2 closely ngage these edges'and uniformly locate the switch housing on the end wall of the rheostat housing.

The construction shown and described therefore permits the switch actuating member I to have a comparatively small clearance from the inner face of the cylindrical side wall of the switch housing 6|. This is important in that the ribs 64 need not extend a great distance inwardly to insure the effectiveness of their inner ends 66 as limiting stops for movement of the member 5| away from vthe .variable resistance housing end wall 43 and also as locating stops during assembly of the parts. By limiting the inward extension of the ribs 64, the actuating lug 53 on plate 5| may be spaced further from the shaft axis allowing a greater operating radius for engaging the switch operating cam 14. With any given location of the operating cam the actuating lug can be made wider in a radial direction by limiting the inward extension of the ribs 54 and therefore additional strength can be provided for the lug to prevent nthe possibility of these lugs bending or fracturing with extensive use.

The accurate spacing of the switch housing in respect to the centrally located bearing hole in the rheostat housing and also in respect to the operating shaft intertted in this bearing hole insures uniform engagement on all controls between the lug 53 and the coacting horns 80 and 8| on the switch operating cam 14. This is very important since the pivot 68 of the cam 14 is located between horns 8|) and 8| and the axis cf rotation of the actuating lug 53 and as the horns 80 and 8| are` also inside the arc of movement of the lug 53 the depth of the horns must necessarily be relatively small to permit transient engagement between the lug and the horns. Accurate and uniform assembly of the parts is therefore highly important.

In a combination variable resistance and switch with a bearing provided in the end wall of -the rheostat housing to facilitate the accurate alignment of the switch and actuating member, it is impossible to absolutely align this bearing in commercial production with the bore in the mounting bushing due to slight variations in the assembly of the mounting bushing l1 in the base and in the assembly of the rheostat housing upon the base. For this reason the bearing area of the shaft in the mounting thimble I1 is reduced as shown at 23 and located adjacent the lower end of the bushing and, together with the clearance 24`between the shaft and the remainder of the bore in the thimble, permits adequate angular displacement of the shaft so that the inner bearing 33 may be tted into the bearing 48a in the rheostat housing end wall without causing the parts to bind.

This shaft bearing arrangement is important in keeping down the cost of production of my improved variable, resistance-switch unit. Formerly, the aligning of two such bearings in a variable resistance was accomplished by increasing the diameter of the bore of the thimble except for a small bearing portion in its lower end, as disclosed in my pn'or Patent No. 2,059,712. This prior structure, while having certain merits, has been found to be expensive due to the fact that a second counter-boring operation on each thimble is necessary to enlarge the upper portion of the bore and as this second operation has to be done on a hand screw machine, the cost of making the thimble is considerably increased. By making my present thimble with a bore of uniform diameter, all the work on it is performed on an automatic screw machine at low cost when the rest of the thimble is being made. I am thus able to make my improved shaft at no additional cost as the reduced clearance section 22a is formed by the automatic screw machine at the same time that the associated C-washer groove is being formed. A further advantage is inherent in my present construction over that yshown in my prior Patent No. 2,059,712. In the construction of the prior patent, the thimble due to its increased bore, and consequently thinner side wall, is liable to be deformed when the usual clamping nut is employed and tightened to secure the device on a radio chassis. Such deformation will frequently cause the shaft to bind and may cause the threads on the thimble to be stripped. Also, when the swaging operation is performed on the shoulder 2| of thimble to secure the spacing washer 20 in position, the bore of the thimble is sometimes objectionably decreased also-resulting in shaft binding.

Where it is not feasible to provide a bearing surface in the upper part of the variable resistance housing, I contemplate a structure wherein the shaft is relieved so as to be supported in contact only with the two end portions of the thimble. By these constructions I am able to employ a thimble with side walls of undiminished cross section, the better to resist distortion of the thimble walls by the tightening of the'clamping nut, and the distortion incident to the swaging operation whereby certain structural elements are secured to the thimble.

The switch actuator is made either of thin metal or of insulating material, preferably the former due to its greater strength and its lower cost. This actuator is a part of the switch mechanism and it is located entirely within the switch housing along with the other switch parts.

As has been stated above, the switch actuator is prevented from rattling in its nest by a film of grease which causes the actuator to adhere closely to the variable resistance housing end wall. Rotative movement of the actuator operates to keep this grease evenly distributed between the actuator and the variable resistance housing end wall and in addition acts as a lubricant to reduce frictional engagement between the actuator and the variable resistance housing end wall. This grease lm further constitutes a reservoir of lubricant which, due largely to the rotative movement of the actuator and to the action of gravity, is fed to the shaft bearing in the variable resistance housing end wall thereby keeping said bearing amply supplied with lubricant.

While it is desirable to avoid play between the shaft 22 and the switch actuator as much as possible so as to assure positive operation of the snap switch at the desired point in the rotary movement of the vshaft and actuator, it is irnportant that the connection be such as will permit sliding movement between the shaft and actuator in a direction parallel to the shaft axis to facilitate assembly and prevent binding of the parts in use. The form of construction shown, with the oblong or substantially rectangular opening 52 in the actuator 5l receiving theflattened portion 49 of the shaft 22 is one eiicient and simple method of providing such a connection.

It will be apparent in the construction shown and described that all of the elements of the switch itself, including the switch operating cam, are located wholly within the switch housing and that no parts of the switch extend within the variable resistance housing or chamber. The end wall of the variable resistance housing has no opening therein with the exception of the central opening with the extruded portion 48 having the bearing 48a therein, and the rectangular slots 63 for receiving the ears 62 on the switch housing 6I. The portion 33 of the shaft'22 completely closes the central opening since it makes a relatively close fit with the bearing wall 48a, and further, the shoulder 3i on the shaft extends outwardly under the extruded portion 48. The

ears 62, as has been previously described and as is clearly shown in Figures '7 and 8, engage the inner edges of the elongated slots 63 so that there are no uncovered openings at these points between the switch housing and variable resistance .i

housing. Should there be any`slight clearance at this point due to variations in manufacture, the fact that the ears 62 are bent inwardly and upwardly against the under face of the wall 43 insures that any such clearances will be fully covered. There is, therefore, a complete metallic wall between the switch and variable resistance, which wall serves as an eifective electrostatic shield to prevent passage of any interfering radiation` from the switch to the variable resistance.

In addition, the switch housing 6i is made of metal and is effectively grounded by means of its connection to the grounded variable resistance housing 42. by the side walls of its housing against lateral radiation and also against radiation in the direction away from the variable resistance by the end wall 65 of the housing 6i which extends over the outer face of the switch base, as shown in Figure 5. The metallic switch housing 6I in cooperation with the completely closed end wall of the variable resistance housing 42 encloses the switch in a grounded electrostatic shield preventing interference radiation from the switch to the terminals I3, I4 and 4|, as clearly appears in Figure 1, and is also very effective in preventing radiation from the switch from reaching any sensitive circuits in the radio receiver or other apparatus with which the control is associated.

Attention is directed to the fact that the switch is shielded from the resistance by the stationary end wall of the resistance housing and that the rotatable switch actuator, although it is preferably formed of metal, has no shielding function whatsoever.

The chamfered end portions 50 and "a of the shaft 22 are desirable in that they facilitate assembly of the parts. The chamfer 50 on the two round-,ed ends of the fiattened portion of the The switch is effectively shielded shaft assists the entry of the shaft into the extruded bearing 48a, while the chamfer on all four sides of the flattened portion 49 facilitates entry of this fiattened portion into the opening 52 in the actuating member 5I.. This chamfer makes it possible to quickly assemble the parts although they may not be accurately aligned when brought together for assembly.

The fact that the switch operating cam 14 is located wholly within the switch housing and does not extend down into the variable resistance housing, results in an appreciable reduction in necessary overall depth of the assembly. This is for the reason that in such combination units when the switch cam extends into the variable resistance housing, that housing must be deeper to provide room for the cam and also-for the switch actuating pin or lug rotated by the variable resistance shaft in that housing.

While I have shown a preferred embodiment of my invention, it is to be understood to be illustrative only as it is capable of change and modification to meet differing conditions and requirements, and I contemplate such variations as come within the spirit and scope of the appended claims. I claim:

1. In a combination variable resistance and snap switch device, a housing for the variable resistance having a fiat metallic end wall, a housing for the switch mounted upon said end wail, a disc like switch actuator constrained to rotary motion within the switch housing for operating the switch, a rotatable shaft adapted for operating the variable resistance and switch, said shaft extending within the variable resistance housing and having an end portion extending through the end wall of the variable resistance housing into the switch housing, a nonrotatable but freely slidable driving connection between said shaft end portion and the switch actuator within the switch housing for transmitting rotary movement from the shaft to the actuator while enabling quick engagement and disengagement between the shaft and the switch actuator, a switch operating cam eccentrically located within the switch housing, and means carried by the switch actuator for making transient driving engagement with said cam to eiect operation of the switch.

2. In a combination variable resistance and snap switch device, a housing for the variable resistance having a fiat end wail, a housing for the switch mounted upon said end wall, the switch having an eccentrically located switch operatingv cam within the switch housing and extending toward the end wail of the variable resistance housing, a at switch actuator plate rotatably supported upon the end wall of the variable resistance housing within the switch housing, means for maintaining the actuator plate adjacent to said end wall, a rotatable shaft adapted for operating the variable resistance and switch, said shaft extending within the variable resistance housing and having an end portion extending through said end wall of the variable resistance housing and into the switch housing, a nonrotatable but slidable driving connection between said shaft end portion and the switch actuator within the switch housing for transmitting rotary movement from the shaft to the actuator while enabling quick engagement and disengagement between the shaft and the switch actuator. and means carried by the switch actuator for making transient driving engagement with the switch cam to effect operation of the switch.

3. In a combination variable resistance and switch device, a base assembly for said variable resistance unit, a rotatable shaft extending through the base, a metallic housing for said variable resistance unit secured to the base, a switch housing secured to the end wall of the variable resistance housing, a-switch within said switch housing, said switch including an operating member, a fiat rotatable switch actuating member upon the outer face of the end wall of the variable resistance housing and within the switch housing, an adhesive lubricant between the switch actuating member and the end wall of the variable resistance housing, said lubricant serving .normally to hold the actuating member against said end wall, said actuating member havingmeans thereon for making transient drivingengagement with the switch operating member, the end wall of the variable resistance housl ing having an opening therein, and a driving connection between the shaft and switch actuating member through said opening.

4. In a combination variable resistance and switch device, a base assembly for said variable resistance, a rotatable shaft extending through the base, a metallic housing for said variable closure for the switch to electrostatically shield i the switch from the variable resistance unit, a plate like switch actuating member constrained to rotation in a plane within said enclosure and closely overlying the outer face of said end wall of the variable resistance unit housing, cooperating means on said switch actuating member and the switch operating member transiently engageable to operate the switch as said actuating member is rotated, and a rotation imparting driving connection between the rotatable shaft and the switch actuating member adjacent to the opening in the end wall of the variable resistance unit housing.

6. In a combination variable resistance and snap switch device, a base assembly for said variable resistance unit, a rotatable shaft extending through the base, a housing for said variable resistance secured to the base, a metallic switch housing secured to the end wall of said variable resistance housing, said switch housing having a lateral cylindrical metallic wall directly contacting and substantially perpendicular to the resistance secured tothe base, a switch housing secured'to the end wall of the variable resistance housing, a switch within said switch housing, said switch including an operating member, a fiat rotatable switch actuating member upon the outer face of the end wall of the variable resistance housing and within the switch housing, an adhesive lubricant between the switch actuating member and the end Wall of the variable resistance housing, said lubricant serving normally to hold the actuating member against said end wall, the actuating member having openings therein to distribute the lubricant, means on said actuating member for making transient driving engagement with the switch operating member, the end wall of the variable resistance housing having an opening therein, positive means for limiting movement of the switch actuating member away from the outer face of the end Wall of the variable resistance housing, and a driving connection between the shaft and switch actuating member through said opening in the v variable resistance housing end wall, said connection transmitting rotary movement from the shaft to the actuator without substantial lost motion and permitting a sliding movement of the actuator relative to the shaft in a. direction parallel to the shaft axis.

5. In a combination variable resistance unit and snap switch device, a base for the variable resistance unit, a rotatable shaft extending through the base for operating the variable resistance unit, a substantially cup-shaped metal housing for the variable resistance unit secured to the base, said housing having an opening in its end wall providing a bearing for the shaft so that the shaft closes the opening and is exposed on the exteriorof said end wall, a snap switch including an operating member, a substantially cup-shaped metal switch housing positively secured to the variable resistance housing with its open side facing the variable resistance housing and completely closed by the end wall of the variable resistance housing so that the shaft is accessible to the interior of the switch housing and said switch housing and end wall with the shaft in its opening form a complete metal enend wall of the variable resistance housing, a switch within said switch housing, said switchv including an operating member, a circular rotatable switch actuating member Vriding on the outer face of the end wall of the variable resistance housing with the edge of the circular actuating member adjacent to the inner face of the cylindrical switch housing wall, means on said cylindrical wall extending inwardly over the switch actuating member to limit movement thereof away from said end wall of the variable resistance housing, and means on the actuating member drivingly engageable with the switch operating member, the wall'of the variable resistance housing having an opening therein, and a driving connection between the rotatable shaft and the switch actuating member adjacent said opening. Y

7. In a combination variable resistance and snap switch device, a base assembly for said variable resistance unit, a metallic housing for said variable resistance secured to the base and having an end wall overlying the base, a metallic switch housing secured to said end wall, said ing, a substantially circular rotatable switch actuating member riding on the outer face of the end wall of the variable resistance housing within the switch housing and with its edge adjacent to the inner face of the cylindrical switch housing wall, portions of said wall extending inwardly of the housing and over the switch actuating memberto limit movement thereof away from the end wall of the variable resistance, housing, said inwardly extending wall portions also engaging the switch supporting lnonfconducting member to retain the same against' the inner face of the switch housing end wall, means on the actuating member adapted to have transient driving engagement with the switch operating member, the end wall of the variable resistance housing having an opening therein, a rotatable operating shaft for the resistance and switch, said shaft having an end portion received in vand closing said opening, and a nonrotatable but freely slidable driving connection between said shaft and the switch actuating member for transmitting rotary movement from the shaft to the actuating member while enabling free relative axial motion between the shaft and actuating member.

8. In a combination variable resistance and snap switch device, a housing completely enclosing the variable resistance, said housing including a substantially flat metal end wall having a hole therethrough, a substantially cup-shaped metal switch housing enclosing the switch and mounted on said end wall of the variable resistance housing with the side wall of the switch housing .directly contacting and substantially perpendicular to said end wall so that said end Wall constitutes a metal partition between the two housings wholly imperforate except for said one opening providing an electrostatic shield b etween the switch and the variable resistance, said switch having an operating member eccentrically disposed with relation to said opening and disposed wholly within said switch housing, a disclike switch actuating member wholly within the switch housing constrained to rotation in a plane adjacent to said end wall upon assembly of the switch housing to the variable resistance housing, said actuating member having a portion adjacent to the hole in the end wall, means on said actuating member transiently engageable with the switch operating member upon rotation of the actuating member, a single shaft for the resistance and switch entering the resistance housing and havingan end portion closing said hole in the resistance housing end wall, and a nonrotatable but axially slidable driving connection between said end portion of the shaft and the switch actuating member.

9. In a combination variable resistance and snap switch device, flatwise spaced opposed walls,

a variable resistance element carried by the inner face of one wall, switch mechanism carried by the inner face of the other wall, means connected with said walls and spanning the intervening space therebetween, said means holding the walls properly spaced and coacting therewith to enclose said resistance element and switch mechanism, an operating shaft rotatably supported from one wall with its inner end projecting into the space between the walls, and intermediate electrostatic shield in the form of a wall permanently connected with said spacing means to divide said housing into a variable resistance element enclosing section and a switch mechanism enclosing section, said intermediate Wall being imperforate except for a single substantially centrally located opening in which the shaft is received with the shaft contacting the edge of the opening `to close the same, a substantially fiat switch actuating disc within the switch mechanism enclosing section and closely overlying said intermediate wall, means onsaid disc operable upon rotation thereof to actuate the switch mechanism, a nonrotatable driving connection between the shaft and the disc, and means actuated by the shaft for varying the effective resistance of the variable resistance element.

NEWTON C. SCHELLENGER. 

